Autonomous Solar Thermo Pump for Lift Irrigation

Abstract

Introduction I the less-developed, arid plains of the Third World where agriculture depends to a large extent on lift irrigation, the sun shines almost invariably whenever water is needed for irrigation, and it seems only proper to utilize this nondepletable source of energy for priming irrigation pumps. The demand in these regions for smalland medium-sized solardriven water pumps, in the kilowatt range, would be enormous if only they could be manufactured cheaply enough. Water pumps may be operated with solar energy directly converted into electricity, or by using heat engines run by the sun's thermal energy suitably trapped in flat-plate or concentrating collectors. While direct conversion of solar energy into electrical energy is not considered economically viable in the context of water pumping, a variety of solar thermal water pumping devices have been developed and demonstrated over the years in several countries, notably in France and the U.S. ~ These are essentially of the heat-engine type, operating between a hot reservoir supplied by the solar collector and a cold reservoir supplied by the ambient air or pumped water. Conventional Rankine cycle power units ranging in power from fractions of a kilowatt to several kilowatts are in limited commercial production in some industrially advanced countries, but their costs are very high. Extensive research and development are underway to bring the costs down. In recent years, increased attention is also being given to the development of simple and special designs of solar water pumps which could be manufactured inexpensively in the developing countries. This paper reports on one such design currently being developed at the St. Augustine Campus of the University of the West Indies, Trinidad.